Hornworms undergo a complete metamorphosis, transforming from a caterpillar into a moth. Recognizing when a hornworm is ready to pupate is important for observers, allowing for proper preparation and a successful transition. This stage marks the shift from the feeding larval form to the quiescent pupal stage.
The Hornworm Life Cycle
The hornworm life cycle involves four distinct stages: egg, larva, pupa, and adult moth. It begins when a female moth lays tiny, spherical green eggs, typically on host plant leaves. These eggs hatch within a few days, giving rise to the familiar caterpillar larval stage. Hornworm larvae are voracious eaters, growing rapidly over two to four weeks and molting several times, reaching up to 3 to 4 inches. Once full-sized, the larva prepares for pupation, burrowing into the soil where it transforms into a pupa; this stage can last for weeks or months, depending on environmental conditions, before the adult moth emerges.
Key Indicators of Pupation
As a hornworm approaches pupation, it exhibits several observable changes.
Physical Changes
One physical change is a significant increase in size, with mature larvae often reaching over 2.75 inches (7 cm) long. Their color may shift from a vibrant green to a duller, yellowish hue as they clear their digestive tract. The skin might also appear tighter or smoother, and a dark, pulsating line, known as the dorsal aorta, can become visible along their back.
Behavioral Changes
Behaviorally, a hornworm ready to pupate will dramatically reduce or completely stop feeding. It becomes restless, beginning a “wandering stage” in search of a suitable place to burrow. This wandering can last for a day or two. If provided with a substrate, the caterpillar will start digging and burrowing into it. Another common sign is the adoption of a “J-shape” or “humped” posture before it burrows.
Preparing for the Pupation Stage
Once a hornworm displays signs of pupation readiness, providing an appropriate environment is important for its successful transformation. A suitable substrate is necessary, as hornworms typically burrow into the soil in nature. Options include loose soil, coco fiber, vermiculite, or shredded paper. The substrate should be deep enough, ideally 3 to 4 inches, to allow the hornworm to fully burrow and create its pupal chamber. The container housing the hornworm should be adequately sized and provide good ventilation. Maintaining appropriate moisture levels in the substrate is also important; it should be moist but not waterlogged to prevent desiccation of the developing pupa and support proper moth development. Placing the container in a dark, undisturbed area can further mimic their natural underground pupation site.
The Pupation Process and Beyond
After burrowing into the substrate, the hornworm undergoes its final larval molt to transform into a pupa. This pupa is typically dark brown, elongated, and oval-shaped, measuring about 45 to 60 mm in length. A distinctive feature of the hornworm pupa is a sheath that projects from the head and curves downward, resembling a pitcher handle. During this stage, the pupa appears rigid but can wiggle its abdomen when gently touched. The pupal stage typically lasts two to four weeks under favorable conditions, but if conditions are not optimal, such as cooler temperatures or shorter day cycles, the pupa may enter a dormant state called diapause, extending this stage for several months before the adult hawk moth emerges from the pupal case.